The present invention relates to a hill hold for a vehicle, and more particularly to a hill hold employing a machine in an electric or hybrid electric vehicle.
Conventionally, an automotive vehicle that is temporarily stopped on an incline can be kept from rolling backwards by an engine providing a low level of torque to a torque converter coupled to an automatic transmission or by a clutch coupled to a manual transmission. Of course, the vehicle brakes can be employed as well, but there are situations when the vehicle operator wants to maintain the vehicle position without engaging the brakes. These situations may arise when a vehicle is stopped at a traffic light or stop sign on a hill and the vehicle operator is preparing to accelerate the vehicle through the intersection.
Electric and hybrid electric vehicles are now coming into use where the engine, if there is one, does not always operate while the vehicle is temporarily stopped. In these vehicles, the vehicle operator may also wish to maintain the vehicle position on an incline without employing the brakes. Some have attempted to accomplish this through various mechanical means, while others have attempted to employ a motor to hold the vehicle in place. In order to hold the vehicle in place with the motor, it operates at zero speed but must maintain just enough torque to hold the vehicle from rolling backwards. When operating under this condition, the motor and inverter will use energy stored in the batteries and may experience significant localized heating concerns. Since the traveling range of electric vehicles is somewhat limited due to battery energy storage limitations, it is desirable to use the least amount of energy as possible. Also, with the motor operating at zero rotation, which is not the normal mode of operation, some components within the electric drive circuitry may experience more heat than is desirable.
Thus, it is desirable to employ a machine in an electric or hybrid electric vehicle that is capable of maintaining a vehicle in a stopped position on an incline, while also minimizing the total power loss (energy used) and distributing the power in order to minimize the heat concentration on individual components of the machine and inverter.
In its embodiments, the present invention contemplates a method of maintaining a vehicle in a stopped position on an incline comprising the steps of: coupling a machine with at least a first phase, a second phase, and a third phase to at least one drive wheel of the vehicle; selectively supplying energy to the first phase, the second phase and the third phase with a pulse width modulated inverter having at least a first half-bridge coupled to the first phase, a second half-bridge coupled to the second phase, and a third half-bridge coupled to the third phase; and maintaining a torque in the machine at an approximately zero rotational speed by switching the inverter between one of: a mode 1 for a first percentage of a pulse width modulated switching period and a mode 7 a remaining percentage of the pulse width modulated switching period; a mode 2 for the first percentage of the pulse width modulated switching period and the mode 7 the remaining percentage of the pulse width modulated switching period; and a mode 6 for the first percentage of the pulse width modulated switching period and the mode 7 for the remaining percentage of the pulse width modulated switching period.
The present invention further contemplates a method of maintaining a vehicle in a stopped position on an incline comprising the steps of: coupling a machine with at least a first phase, a second phase, and a third phase to at least one drive wheel of the vehicle; selectively supplying energy to the first phase, the second phase and the third phase with a pulse width modulated inverter having at least a first half-bridge coupled to the first phase, a second half-bridge coupled to the second phase, and a third half-bridge coupled to the third phase; and maintaining a torque in the machine at an approximately zero rotational speed by: switching the inverter between a mode 1 for a first percentage of a pulse width modulated switching period and a mode 7 a remaining percentage of the pulse width modulated switching period, for about a first one third of a predetermined time period, with the predetermined time period being at least three times longer than the pulse width modulated switching period; switching the inverter between a mode 6 for the first percentage of the pulse with modulated switching period and a mode 8 the remaining percentage of the pulse width modulated switching period, for about a second one third of the predetermined time period; and switching the inverter between a mode 5 for the first percentage of the pulse width modulated switching period and the mode 7 the remaining percentage of the pulse width modulated switching period, for about a third one third of the predetermined time period.
An embodiment of the present invention also contemplates a hill hold apparatus. The hill hold apparatus includes a machine adapted to couple to and drive at least one drive wheel of the vehicle, with the machine including at least a first phase, a second phase, and a third phase. A pulse width modulated inverter has at least a first half-bridge coupled to the first phase, a second half-bridge coupled to the second phase, and a third half-bridge coupled to the third phase, with the inverter adapted to connect to a source of electrical energy. A machine controller is connected to and adapted to control first half-bridge, the second half-bridge and the third half-bridge of the inverter, and includes a hill hold strategy for controlling the inverter to maintain a torque in the machine at an approximately zero rotational speed by switching the inverter between one of: a mode 1 for a first percentage of a pulse width modulated switching period and a mode 7 a remaining percentage of the pulse width modulated switching period, a mode 2 for the first percentage of the pulse width modulated switching period and the mode 7 the remaining percentage of the pulse width modulated switching period; and a mode 6 for the first percentage of the pulse width modulated switching period and the mode 7 for the remaining percentage of the pulse width modulated switching period.
An advantage of an embodiment of the present invention is that the power losses from the inverter are at or near minimum during hill hold operation, while evenly distributing the power losses among the inverter power switches in order to avoid overheating concerns.
Another advantage of an embodiment of the present invention is that the heat distribution among the machine phases will be relatively balanced, thus minimizing any possible load unbalance. By reducing the possible load unbalance due to uneven heating of the phases, the controller need not be programmed to account for this complexity.